1. Field of the Invention
The present invention relates to ceramic composite materials employed as die materials for the transfer molding of glass, resins, ceramics, and similar substances. In particular the present invention relates to such ceramic composites having excellent mechanical and thermal properties.
2. Description of the Background Art
In matched die molding as the basis of forming operations, improving the die release between the dies and the material that is being molded by them has always been crucial.
For example, Japanese Unexamined Pat. App. Pub. No. 2001-100016 discloses a means for separating mold components and the molded material by exploiting the difference in their respective thermal expansion coefficients. However, the die materials selected for this method are conventional, well-known materials, most of which have low heat resistance, which has led to problems in practical use.
Japanese Unexamined Pat. App. Pub. No. 2003-63832 discloses a die material designed so that the linear thermal expansion coefficient of the die material is lower than the linear thermal expansion coefficient of the molded material. The die material in this case is a glass material, which places a limitation on the temperature range or pressure at which the die material can be used, thus presenting problems in practical use. A further problem is that determining the thermal expansion coefficient of the die material according to the form of the glass, resin, or ceramic material that is actually to be molded is critical, which has led to demands for die materials that allow the thermal expansion coefficient to be controlled.
Methods based on compositing are effective as means for controlling the thermal expansion coefficient.
For example, Japanese Unexamined Pat. App. Pub. No. 2003-34580 discloses a material with excellent friction properties and wear resistance, composed of a composite material of silicon nitride, titanium nitride, and 0.5 to 20 wt. % graphite and carbon. However, from an attempt to sinter the powder under the conditions described in this patent publication it was evident that the product could not be used for dies because the filling density was a low 93%, numerous pores with a diameter of 20 μm or more were discerned in observations made using SEM at a magnification of 2000×, and density was insufficient.
Another compositing example, reported in Japanese Unexamined Pat. App. Pub. No. S60-100646, is a highly tough material in which C, Cr, Mo, W, Al, Ti, and Ni are incorporated at 0.5 to 6 wt. % as an oxidation-resistant alloy into an alumina and zirconia powder. However, the carbon content is a slight 0.1 to 0.2 wt. %, and thus the material lacks the lubricity required of a die.
In turn, Japanese Unexamined Pat. App. Pub. No. H09-87029 reports that a material obtained by adding 2 to 50 wt. % carbon with a particle size of 5 μm or more to silicon carbide has excellent wear resistance, and reported in Japanese Unexamined Pat. App. Pub. No. H05-301773 is a material in which 3 to 30 wt. % graphite with a mean particle size of 3 to 6 μm is dispersed in a titanium carbide matrix.
However, these materials have a large mean particle diameter of carbon of 3 μm or more, and in machining the materials into desired form, the surface roughness is affected by the particle diameter, which is prohibitive of producing mirrorlike surfaces—a surface roughness (Ra) of 50 nm or less—on the formed materials.
Japanese Unexamined Pat. App. Pub. No. H10-231174 describes a material in which graphite and boron nitride are dispersed in a non-oxide ceramic, and iron oxide, iron silicide, or a similar iron compound is interposed at the boundary layer. However, this material is not suitable for dies because of oxidation-induced deterioration owing to the inclusion of iron and because of the lack of stability at high temperatures.